ELECTROENCEPHALOGRAPHY (EEG) EEG

 The electroencephalogram (EEG) is a recording of the electrical activity of the from the scalp.

 The first recordings were made by in 1929 Origin of EEG waves Electroencephalogram

 EEG is the record of electrical activity of brain( superficial layer i.e. the of pyramidal cells) by placing the electrodes on the scalp. Intracranial EEG (ECoG) Intracranial EEG (ECoG) Objectives of EEG practical

 Familiarize with the principles of techniques involved  Count frequencies and measure the amplitudes of the record obtained.  Categories the records into appropriate rhythms – α, β, θ,and δ.

Cont… Objectives of EEG practical

 Identify and describe changes produced by provocation tests. e.g. eye opening & closing, intermittent photic stimulation (IPS) clapping sound, induce thinking & hyperventilation.  Appreciate clinical uses of EEG EEG Waves

-- 8 – 13 Hz.  -- >13 Hz. (14 – 30 Hz.)  -- 4 – 7.5 Hz.  Delta waves – 1 – 3.5 Hz. ▪ D T A B Different types of brain waves in normal EEG EEG Recording From Normal Adult Male Alpha wave

 rhythmic, 8-13 Hz  mostly on occipital lobe  20-200 μ V  normal,  relaxed awake rhythm with eyes closed Beta wave

 irregular, 14-30 Hz  mostly on temporal and frontal lobe  mental activity  excitement Theta wave

 rhythmic, 4-7 Hz  Drowsy,

 slow, < 3.5 Hz  in adults  normal sleep rhythm

Different types of brain waves in normal EEG

Rhythm Frequency Amplitude Recording (Hz) (uV) & Location Alpha(α) 8 – 13 50 – 100 Adults, rest, eyes closed. Occipital region

Beta(β) 14 - 30 20 Adult, mental activity Frontal region

Theta(θ) 5 – 7 Above 50 Children, drowsy adult, emotional distress Occipital Delta(δ) 2 – 4 Above 50 Children in sleep

D T A B Requirements

 EEG machine (8/16 channels).  Silver cup electrodes/metallic bridge electrodes.  Electrode jelly.  Rubber cap.  Quiet dark comfortable room.  Skin pencil & measuring tape. Computerized EEG Machine EEG Electrodes

Sliver Electrodes Electrodes Cap Procedure of EEG recording

 A standard EEG makes use of 21 electrodes linked in various ways (Montage).  Apply electrode according to 10/20% system.  Check the impedance of the electrodes. 10 /20 % system of EEG electrode placement EEG Electrodes

 Each electrode site is labeled with a letter and a number.  The letter refers to the area of brain underlying the electrode e.g. F - Frontal lobe and T - Temporal lobe.  Even numbers denote the right side of the head and  Odd numbers the left side of the head. Two types of recording

 Bipolar – both the electrodes are at active site ◼ Bipolar montage are parasagital montage.  Unipolar – one electrode is active and the other is indifferent kept at ear lobe.  Always watch for any abnormal muscle activity.  Ask the subject to open eyes for 10 sec. then ask them to close the eyes.

Montage

 Different sets of electrode arrangement on the scalp by 10 – 20 system is known as montage.  21 electrodes are attached to give 8 or 16 channels recording. Analysis

 Electrical activity from the brain consist of primarily of rhythms.  They are named according to their frequencies (Hz) and amplitude in micro volt (μv).  Different rhythms at different ages and different conditions (level of )  Usually one dominant frequency (background rhythm) Factor influencing EEG

 Age ◼ Infant – theta, delta wave ◼ Child – alpha formation. ◼ Adult – all four waves.  Level of consciousness (sleep)  Hypocapnia(hyperventilation) slow & high amplitude waves.  Hypoglycemia  Hypothermia Slow waves  Low glucocorticoids NORMAL EEG CHANGES Desynchronization or Alpha block

 Cause:  Eyes opening (after closure)  Thinking by the subject (mathematical calculation)  Sound (clapping) Eye opening

 Alpha rhythm changes to beta on eye opening (desynchronization / α- block) Thinking

 Beta waves are observed Provocation test

 Intermittent photic stimulation  Increase rate & decrease amplitude

 Hyperventilation  Decrease rate & increase in amplitude Use of EEG  ▪ Generalized (grandmal) seizures. ▪ Absence (petitmal) seizures.  Localize brain tumors.  Sleep disorders () ▪ ▪ syndrome ▪ and  Helpful in knowing the cortical activity, toxicity, hypoxia and encephalopathy &  Determination of brain death. ◼ Flat EEG(absence of electrical activity) on two records run 24 hrs apart. Sleep studies

 The EEG is frequently used in the investigation of sleep disorders especially sleep apnoea.  Polysomnography : EEG activity together with ◼ heart rate, ◼ airflow, ◼ respiration, ◼ oxygen saturation and ◼ limb movement Sleep patterns of EEG  There are two different kinds of sleep:  (REM-Sleep)  Non-REM sleep (NREM sleep)/ slow wave sleep  NREM sleep is again divided into 4 stages (I to IV). The EEG pattern in sleep is given in the following table: Stages of sleep EEG pattern Somatic or Behavioral changes Alert Alpha activity on Respond to verbal eye closed commands Desynchronization on eye opening I (Drowsiness) Alpha dropout & Reduced HR & RR appearance of vertex waves & theta. II (Light sleep) Sleep spindles, Reduced HR & RR vertex sharp waves & K- complexes III ( Deep Sleep) Much slow Reduced HR & RR background K- complexes IV (very deep Synchronous delta Reduced HR & RR sleep) waves, some K- complexes

REM sleep Desynchronization HR, BP & RR irregular (paradoxical with faster Marked hypotonia sleep) frequencies Rapid eye movement 50 – 60 /min. Dreaming threshold of arousal